1. Field of the Invention
The present invention relates to a photochromic film having a photochromic activity to develop or change color by exposure to light, and more specifically, it relates to a durable photochromic film retaining said photochromic activity for a long time.
2. Description of the Prior Art
There have previously been well known so-called photochromic materials which absorb light in the UV region to develop or change color and fade color when UV rays are shut out.
Photochromic products in the form of a thin plate incorporating such a photochromic material in a resin binder sandwiched between glasses have widely been used in glasses for automobiles, glazings, etc. (for example, see JUA No. 50110/89).
However, the conventional photochromic products could not retain the unique activity of photochromics which develop or change color by exposure to light. Particularly when used outdoors during summer, the product life was shortened.
We investigated the cause of the above problem and found that photochromic materials deteriorate by contact with heat, oxygen and moisture, particularly oxygen in addition to exposure to UV rays. Particularly when used under high temperature and high humidity conditions, photochromic materials rapidly deteriorated.
Accordingly, an object of the present invention is to provide a highly durable photochromic film retaining a photochromic activity for a long time even when used under high temperature and high humidity conditions.
In order to attain the above object, the present invention provides a durable photochromic film comprising a coloring material layer containing a photochromic material and a phototransmissive deposition film laminated to said coloring material layer.
The present invention also provides a durable photochromic film wherein said deposition film is laminated to each side of said coloring material layer.
The present invention further provides a durable photochromic film wherein said deposition film has oxygen permeability of 0.5 (cc/m2.day.atm) or less when a polyolefin film is laminated to each face of said deposition film.
According to the present invention, the coloring material layer consisting of a photochromic material and a base polymer is protected by the phototransmissive deposition film.
Namely, the phototransmissive deposition film is permeable to UV rays to retain the photochromic activity. The deposition film as a whole has low oxygen permeability by the presence of the deposit to prevent a photochromic material in the coloring material layer from coming into contact with oxygen and thus can retain the photochromic activity.
Unlike saran resins or ethylene resins previously known as oxygen barrier films, the phototransmissive deposition film according to the present invention does not increase the oxygen permeability or vapor permeability with variation of the environmental temperature used.
Therefore, the photochromic film according to the present invention can retain the photochromic activity for a long time even when it is used under high temperature and high humidity conditions.